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Query: HUMANGGP:009336 (ATPase)
 59,826 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The characterization and localization of a Ca(2+)-ATPase (ATP phosphohydrolase, EC 3.6.1.3) in the tooth germ of the porcine fetus are reported. This enzyme, a microsome fraction, is preferentially activated by Ca(2+). In the presence of 0.5 mM ATP, maximal enzyme activity is obtained at 0.5--1.0 mM CaCl2. The maximal rate of ATP hydrolysis is approx. 20 mumol per h per mg of protein as the enzyme preparation is used here. At optimal Ca(2+) concentration, the Mg(2+) has an inhibitory effect. The enzyme does not require Na+ or/and K+ for activation by Ca(2+). Other nucleotide triphosphates may serve as the substrate, but V for ATP is the highest. The Km for ATP is 8.85 - 10(-5) M. The optimal pH for Ca(2+) activation of the enzyme lies around 9.2. Well known inhibitors of (Na+ + K+)-ATPase, mitochondria ATPase and Ca(2+)-ATPase in the erthrocyte do not inhibit the enzyme. In the subcellular order the enzyme may be assumed to be localized in the smooth endoplasmic reticulum fraction containing cell and Golgi body membrane fragments and in the tissue order in the enamel organ containing an ameloblast layer, stratum intermedium and stellate reticulum.
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PMID:Calcium-stimulated adenosine triphosphatase in the microsomal fraction of tooth germ from porcine fetus. 0 71

1. Based on incorporation of radioactively labeled N-ethylmaleimide, the readily reactive thiol groups of isolated myosin (EC 3.6.1.3) from fast, slow and cardiac muscles could be classified into 3 types. All 3 myosins contain 2 thiol-1, 2 thiol-2 and a variable number of thiol-3 groups per molecule. Both thiol-1 and thiol-2 groups which are essential for functioning of the K+-stimulated ATPase, are located in the heavy chains in all 3 myosin types. 2. The variation in the incorporation pattern of N-ethylmaleimide over the 3 thiol group classes under steady-state conditions of Mg(2+) - ATP hydrolysis allowed different conformations of some reaction intermediates to be characterized. In all 3 types of myosin the hydrolytic cycle of Mg(2+) - ATP was found to be controlled by the same step at 25 degrees C. In all three cases, this rate-limiting step is changed in the same way by lowereing temperature. 3. Using the chemically determined molecular weights for myosin light chains, their stoichiometry was found on the basis of sodium dodecyl sulfate electrophoresis to be 1.2 : 2.1 : 0.8 for light chain-1: light chain-2:light chain-3 per molecule of fast myosin, 2.0 : 1.9 for light chain-1:light chain-2 per molecule of slow myosin and 1.9 : 1.9 for light chain-1:light chain-2 per molecule of cardiac myosin. This qualitative difference in light subunit composition between the fast and the two types of slow myosin is not reflected in the small variations of the characteristics exhibited by the isolated myosins, but rather seems to be connected with their respective myofibrillar ATPase activities.
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PMID:Radioactive labeling and location of specific thiol groups in myosin from fast, slow and cardiac muscles. 0 73

The (Na+ +K+)-activated, Mg2+-dependent ATPase from rabbit kidney outer medulla was prepared in a partially inactivated, soluble form depleted of endogenous phospholipids, using deoxycholate. This preparation was reactivated 10 to 50-fold by sonicated liposomes of phosphatidylserine, but not by non-sonicated phosphatidylserine liposomes or sonicated phosphatidylcholine liposomes. The reconstituted enzyme resembled native membrane preparations of (Na+ +K+)-ATPase in its pH optimum being around 7.0, showing optimal activity at Mg2+:ATP mol ratios of approximately 1 and a Km value for ATP of 0.4 mM. Arrhenius plots of this reactivated activity at a constant pH of 7.0 and an Mg2+: ATP mol ratio of 1:1 showed a discontinuity (sharp change of slope) at 17 degrees C, with activation energy (Ea) values of 13-15 kcal/mol above this temperature and 30-35 kcal below it. A further discontinuity was also found at 8.0 degrees C and the Ea below this was very high (greater than 100 kcal/mol). Increased Mg2+ concentrations at Mg2+:ATP ratios in excess of 1:1 inhibited the (Na+ +K+)-ATPase activity and also abolished the discontinuities in the Arrhenius plots. The addition of cholesterol to phosphatidylserine at a 1:1 mol ratio partially inhibited (Na+ +K+)-ATPase reactivation. Arrhenius plots under these conditions showed a single discontinuity at 20 degrees C and Ea values of 22 and 68 kcal/mol above and below this temperature respectively. The ouabain-insensitive Mg2+-ATPase normally showed a linear Arrhenius plot with an Ea of 8 kcal/mol. The cholesterol-phosphatidylserine mixed liposomes stimulated the Mg2+-ATPase activity, which now also showed a discontinuity at 20 degrees C with, however, an increased value of 14 kcal/mol above this temperature and 6 kcal/mol below. Kinetic studies showed that cholesterol had no significant effect on the Km values for ATP. Since both cholesterol and Mg2+ are known to alter the effects of temperature on the fluidity of phospholipids, the above results are discussed in this context.
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PMID:Alterations in phospholipid-dependent (Na+ +K+)-ATPase activity due to lipid fluidity. Effects of cholesterol and Mg2+. 0 90

Nucleotides have at least two functions in eukaryotic cilia and flagella. ATP, originating in the cells, is utilized for motility by energy-transducing protein(s) called dynein, and the binding of guanine nucleotides to tubulin, and probably certain transformations of the bound nucleotides, are prerequisites for the assembly of microtubules. Besides dynein, which can be solubulized from Chlamydomonas flagella as a heterogeneous, Mg2+ or Ca2+-activated ATPase, we have purified and characterized five other flagellar enzymes involved in nucleotide transformations. A homogeneous, low molecular weight, Ca2+-specific adenosine triphosphatase was isolated, which was inhibited by Mg2+ and was not specific for ATP. This enzyme was not formed by treating purified dynein with proteases. It was absent from extracts of Tetrahymena cilia. Its function might be an auxiliary energy transducer, or in steering or tactic responses. Two species of adenylate kinase were isolated, one of which was much elevated in regenerating flagella; the latter was also present in cell bodies. A large part of flagellar nucleoside diphosphokinase activity could not be solubilized. Two soluble enzyme species were identified, one of which was also present in cell bodies. Since these enzymes are of interest because they might function in microtubule assembly, we studied the extent to which brain nucleoside diphosphokinase co-polymerizes with tubulin purified by repeated cycles of polymerization. Arginine kinase was not detected in Chlamydomonas flagellar extracts.
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PMID:Nucleotide-metabolizing enzymes in Chlamydomonas flagella. 0 Mar 97

A member of a family which was known to be susceptible to malignant hyperpyrexia, who was identified as a carrier by the presence of an elevated serum creatine-phosphokinase, has been investigated further. Muscle was examined biochemically, and the study included the sarcoplasmic ATPase-activity, actinomycin, Mg2+ ATPase activity, ATP, phosphocreatine and glucose-6-phosphate. In addition, the calcium uptake by the sarcoplasmic reticulum was studied. The histochemical analysis of the muscle revealed the presence of a new fibre type characterised by a dense rim of ATPase activity, which gives the impression of a 'picture-frame'. Ultramicroscopic study revealed changes in the mitochondria and areas of myofibrillar disruption with swelling of the sarcoplasmic reticulum.
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PMID:'Picture frame' fibres in a carrier of the trait for malignant hyperpyrexia. 0 Jul 95

The optimal conditions are selected for electron-cytochemical detection of the ATPase activity in nuclei of the skeletal muscles of rabbits and nuclei of Vicia faba L. meristem. It is shown that the previous fixation of nuclei in the rabbit skeletal muscle for 10 min in a mixture of the buffer solutions of 4% glutaric dialdehyde and 4% neutral formalin (1:1) causes a decrease in their ATPase activity by 78% in the medium containing Mg2+ and by 34% - in the medium containing Ca2+; in nuclei of horse bean seedlings meristem it lowers respectively by 28 and 16%. Ions of lead in a concentration of 0.4 mM evoke a decrease in the ATPase activity in the medium containing Mg2+, in nuclei of the rabbit skeletal muscles by 35% and in nuclei of horse bean meristem by 15% in the medium containing Ca2+. The vaule of the residual activity is sufficient for detection of the product of ATP enzymic hydrolysis reaction by activity is sufficient for detection of the product of ATP enzymic hydrolysis reaction by the method of electronic cytochemistry. An increase in the Pb2+ concentration higher than 2.8 mM evokes nonenzymic hydrolysis of ATP. The ATPase activity under the electron-cytochemical study is found within the range of pH 6.3-8.5. The product of reaction forms most intensively at pH 7.2-7.5 in the medium with both Mg2+ and Ca2+.
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PMID:[Determination of optimal conditions for the electron-cytochemical detection of ATPase activity in isolated nuclei]. 0 Aug 36

1. An activator of the (Ca2+ plus Mg2+)-stimulated ATPase present in the human erythrocytes (membrane) has been isolated in soluble form from hemolysates of these cells. Partial purification has been achieved through use of carboxymethyl-Sephadex chromatography. The resulting activator fraction contained no hemoglobin and only 0.3% of the total adenylate kinase activity of the cell. 2. Whereas the activator was released from erythrocytes subjected to hemolysis in 20 miosM buffer at pH 7.6 or at pH 5.8, only the membranes prepared at pH 7.6 were affected by it. 2. Whereas the activator was released from erythrocytes subjected to hemolysis in 20 miosM buffer at pH 7.6 or at pH 5.8, only the membranes prepared at pH 7.6 were affected by it. 3. When (Ca2+ plus Mg2+)-ATPase activity was measured by 32Pi release from (gamma-32P)ATP, freeze-thawed erythrocytes, as well as membranes prepared at pH 5.8 and at pH 7.6, expressed lower values than noted by assay for total Pi release. When ADP instead of ATP was used as substrate, significant amount of Pi were released by these erythrocyte preparations. Further study revealed (a) production of ATP and AMP from ADP with membranes and hemolysate alone, and (b) exchange of the gamma-and B-position phosphate on (gama-32P)ATP in the presence of membranes plus hemolysates. These observations established the presence of adenylate kinase activity in the (membrane-free) hemolysates and in membranes. It further supports the conclusion that Pi release from ADP by human erythrocytes (freeze-thawed) and by their isolated membranes is due to formation of ATP by adenylate kinase and hydrolysis of this generated ATP by (Ca2+ plus Mg2+)-ATPase. 4. The following points were also established: (a) absence of an ADPase in human erythrocytes; (b) the (Ca2+ plus Mg2+)-ATPase activator enhanced cleavage only of the gama-position of ATP and (c) the (Ca2+ plus Mg2+)-ATPase activator is neither adenylate kinase nor hemoglobin.
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PMID:Studies on an activator of the (Ca2+ plus Mg2+)-ATPase of human erythrocyte membranes. 0 Oct 98

TTP accelerated ATP-induced superprecipitation of actomyosin in as low a concentration as 30 muM and decreased light scattering by actomyosin. These effects could also be observed in the same way, but to a lesser degree, by addition to TDP. Myosin was able to hydrolyze TTP to TDP, but some important differences were confirmed between myosin TTPase and ATPase. Myosin TTPase was inhibited by actin and showed a much larger Km than that of ATPase. TTP significantly inhibited myosin B ATPase and ATP greatly inhibited myosin B TTPase. These findings suggest that the accelerating effect of TDP and TTP may be due to the binding of thiamine phosphate to the regulatory site of myosin followed by a change in its physical chemical property, rather than due to the competitive binding of thiamine phosphate to the catalytically activity site of myosin.
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PMID:Thiamine triphosphatase activity of myosin and accelerating effect of thiamine di- and tri-phosphates on superprecipitation of actomyosin. 0 81

An electrochemical potential difference for hydrogen ions ( a protonmotive force) was artifically imposed across the membrane of the anaerobic bacterium Streptococcus lactis. When cells were exposed to the ionophore, valinomycin, the electrical gradient was established by a potassium diffusion potential. A chemical gradient of protons was established by manipulating the transmembrane pH gradient. When the protonmotive force attained a value of 215 mV or greater, net ATP synthesis was catalyzed by the membrane-bound Ca++, Mg++ -stimulated ATPase. This was true whether the protonmotive force was dominated by the membrane potential (negative inside) or the pH gradient (alkaline inside). Under these conditions, ATP synthesis could be blocked by the ATPase inhibitor, dicyclohexylcarbodiimide, or by ionophores which rendered the membrane specifically permeable to protons. These observations provide strong evidence in support of the chemiosmotic hypothesis, which states that the membrane-bound ATPase couples the inward movement of protons to the synthesis of ATP.
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PMID:ATP synthesis driven by a protonmotive force in Streptococcus lactis. 0 50

Active buffer transport, e.g. H+ -secretion by stomach and kidney and HCO3--secretion by pancreas and salivary glands, is linked with the presence of a HCO3-stimulated ATP-Phosphohydrolase. In contrast to (Na+ -k+)-ATPase which is considered to be equivalent to the Na+ pump, the HCO3--ATPase requires only one ion for activation and is insensitive to ouabain. The HCO3--ATPase is found in the plasma membrane of the epithelia, but in contrast to the (Na+ -k+)-ATPase it is located in the luminal cell border. The activity of the HCO3--ATPase changes in parallel along with the rate of active buffer transport, a finding which underlines its importance as a transport enzyme. Several disorders of buffer transport are described which are possibly associated with a defect of the HCO3--ATPase system.
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PMID:[The role of HCO3- ATPase in H+ /HCO3-Secretion (author's transl)]. 0 81


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